b=1852

b=1852
If we leave revalidate_it by returning 0, thus causing a lookup_it call which
re-uses the same request, then we shouldn't drop our reference on the request.

In the past, we accounted for this by doing an addref in mdc_intent_lock in the
-ESTALE case, but this was wrong.  That was just one of many ways that we can
leave revalidate and enter lookup, and this patch fixes that whole class of
erroneous decrefs.